1. Field of the Invention
This invention relates to the field of dynamic pressure type slide bearings and methods of manufacture thereof, and more particularly, to a dynamic pressure type slide bearing in which a metallic outer cylindrical member is integrally joined around a thin walled inner cylindrical member made of synthetic resin having on its bearing bore face a plurality of dynamic pressure generating grooves formed by moulding.
2. Prior Art
Generally, dynamic pressure type slide bearings made of synthetic resin can be readily manufactured by mass production by virtue of the material's good formability. Such mouldings characteristically contact the mating shaft with a fairly low coefficient of friction both during starting and running under low speed. These bearings have been made by the steps of injecting or pouring resilient synthetic resin into a metal mould, and then pulling out the solidified bearing from the metal mould, a step made possible by virtue of the resiliency of the moulded bearing.
However, these synthetic resin bearings have proved to be difficult to mould accurately with respect to both bearing bore size and configuration as a whole. Therefore, they are unsatisfactory for generating the necessary dynamic pressure required for these dynamic pressure type bearings. In addition, due to their high coefficient of thermal expansion, they have poor dimensional stability with respect to bearing bore diameter when subjected to temperature change during operation. Thus, they have not yet been widely applied in actual use.
Conventional dynamic type slide bearings fabricated of synthetic resin, due to the large dimensional variation of the bearing bore diameter and the lack of accuracy in configuration, are liable to have such defects that the face of the bearing bore partially contacts the mating shaft with too strong a force, and/or the action of the grooves for generating dynamic pressure for lubrication becomes nonuniform. Thereby, accuracy of the bearing with respect to bearing run-out, durability and load carrying capacity will become degraded from usage.
In addition, since the conventional bearings vary so greatly in bore diameter and in accuracy of configuration, they cannot be used in applications requiring reduced bearing clearance. Accordingly, their load carrying capacity is low, and the running torque may not be reduced by using low viscosity lubricants. Moreover, since the coefficient of expansion of the bearing bore due to temperature rise during operation is fairly high, bearing clearance of these bearings is inevitably variable.
To make matters even worse, bearings of the conventional type show considerable volumetric shrinkage during moulding. That is, when the synthetic resinous material used therein is cooled, solidified and crystallized, the material shrinks and causes the formed bearing to tightly contact the inner mould. Thus, the corners of the grooves for generating dynamic pressure formed on the bearing bore face are liable to cut into the recessed portions defined between the adjacent ridges of the inner mould for forming the bearing grooves.
A related invention by the same inventor as the inventor of the present invention aims to solve the aforesaid drawbacks and has been filed in Japan as a patent application, published as Laid-Open (unexamined) Patent Publication No. Sho 61(1986)-036516.